In a data switching network, data traffic is categorized into various flows which are stored in a number of queues in a buffer. In a router or other network element, the queues for the stored flows typically compete for a common outgoing communications link or egress port (e.g., a physical communications link or a pseudo-wire). Thus, the buffered queues need to be scheduled on the egress side. Accordingly, processing is required by packet scheduling devices on the egress in the router prior to transmission to select which of the queued packets will be the next in line for outgoing transmission.
Typically, in a routing process, data packets coming in from different source ports are classified based on their source and destination ports and traffic types. They are subsequently sorted into different queues in the buffer. The state of each queue is updated when a packet enters into a queue. Based on the output port availability, the scheduler selects the right scheduling algorithm to dequeue the packets from the corresponding queues. The state of each queue will be updated when a packet moves out of a queue. This process adds latency time in the routing of the data packets in the range of 150 clock cycles.
Additional latency time is incurred in the processing of multicast for classifying of data packets based on their source and destination ports and traffic types, subsequently sorting the data packets into different queues, updating the state of each queue when a data packet enters into the queue, and based on port availability having a scheduler select the right scheduling algorithm to dequeue the packets from the corresponding queues in the buffer, and which has to be repeated separately for each of the data packets replicated. Also, Quality of Service (QoS) algorithmic checks are required for each of the copies of the data packets replicated when there is needed a guarantee of preferential service as in occurrences of high priority traffic, such as control traffic or voice/video latency sensitive traffic, transmissions.
For example, if the incoming data packets are to be broadcast to 128 egress ports, the total latency would be in the range of the latency time per processing cycle of the data packets of 150 clocks cycles increased by a factor related to the 128 egress ports or a latency in the range of 128×150 clock cycles. This increased latency is undesired for some applications.
Accordingly, when transmitting multicast data packets there is a need to bypass and eliminate redundant processing steps to reduce overall latency times associated with the broadcasting of the multicast data packets to multiple ports.